[gtk/fix.ngl.msvc] gskngltexturelibraryprivate.h: Fix build on Visual Studio

[Chun-wei Fan <fanchunwei src gnome org>]

commit 2b6ce3af0fdc985c9f09148a6553d0b2ce457f8e
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Tue Mar 2 14:44:29 2021 +0800

    gskngltexturelibraryprivate.h: Fix build on Visual Studio
    
    The 'GskNglTextureAtlasEntry' structure is used as a member in two other
    structures in two Gsk private headers, namely 'GskNglGlyphValue' and
    'GskNglIconData', but the build breaks on Visual Studio since
    'GskNglTextureAtlasEntry' contains a last member that is a zero-sized array
    that is normally OK if it is the last member of structure -or- if the structure
    that contains a 'GskNglTextureAtlasEntry' structure as its last member.
    Otherwise, a GCCism is involved here.
    
    Fix the build on Visual Studio compilers by not using a zero-sized array as
    a last member of 'GskNglTextureAtlasEntry', on Visual Studio compilers.

 gsk/ngl/gskngltexturelibraryprivate.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
---
diff --git a/gsk/ngl/gskngltexturelibraryprivate.h b/gsk/ngl/gskngltexturelibraryprivate.h
index 56c3d604cc..874eeb769b 100644
--- a/gsk/ngl/gskngltexturelibraryprivate.h
+++ b/gsk/ngl/gskngltexturelibraryprivate.h
@@ -53,6 +53,12 @@ typedef struct _GskNglTextureAtlas
   void *user_data;
 } GskNglTextureAtlas;
 
+#if defined (_MSC_VER) && !defined (__clang__)
+# define NGL_TRAILING_DATA_SIZE 1
+#else
+# define NGL_TRAILING_DATA_SIZE 0
+#endif
+
 typedef struct _GskNglTextureAtlasEntry
 {
   /* A backreference to either the atlas or texture containing
@@ -89,9 +95,11 @@ typedef struct _GskNglTextureAtlasEntry
   /* Suffix data that is per-library specific. gpointer used to
    * guarantee the alignment for the entries using this.
    */
-  gpointer data[0];
+  gpointer data[NGL_TRAILING_DATA_SIZE];
 } GskNglTextureAtlasEntry;
 
+#undef NGL_TRAILING_DATA_SIZE
+
 typedef struct _GskNglTextureLibrary
 {
   GObject        parent_instance;